As the ball spline, there has been known a ball spline including a spline shaft having a plurality of linear spline grooves extending in an axial direction which are formed on an outer peripheral face of the spline shaft, a spline nut provided with ball circulation passages corresponding to the spline grooves of the spline shaft and through which the spline shaft is passed, and a plurality of balls which are disposed in the ball circulation passages of the spline nut, wherein the spline nut includes a nut body which has spline grooves corresponding to the spline grooves of the spline shaft thereby to form main passages, and a cage which is fixed to an inner periphery of the nut body and forms return passages between the cage and the nut body (Reference should be made to Patent Document 1).
In the ball spline as described above, each of the return passages includes a no-load raceway part which is parallel to the main passage, and a connecting part for connecting the main passage and the no-load raceway part, and the no-load raceway part is provided radially outside than the main passage.